Cas9 and Cpf1 can be reprogrammed to different sites or multiple sites using multiple gRNAs. The availability of the different engineered variants of Cas9 and Cpf1 allows for different types of cuts for genome editing, which include the following:

Cut & Revise and Cut & Remove typically result in disruption of a problematic gene or elimination of a mutation. These approaches leverage the cell's natural DNA repair mechanisms known as non-homologous end joining, or NHEJ, to complete the edit.

When a cell repairs a DNA cut by NHEJ, it leaves small insertions and deletions at the cut site, collectively referred to as indels. NHEJ can be used to either cut and revise the targeted gene or to cut and remove a segment of DNA. In the ''cut and revise'' process, a single cut is made. In the ''cut and remove'' process, two cuts are made, which results in the removal of the intervening segment of DNA. This approach could be used to delete either a small or a large segment of DNA depending on the type of repair desired.

The second mechanism our Cut & Replace approach leverages a different DNA repair mechanism known as homology directed repair, or HDR. In this approach, a DNA template is also provided, one that is similar to the DNA that has been cut. The cell can use the template to construct reparative DNA, resulting in the replacement of a defective genetic sequence with the correct one.

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CRISPR | Genome Editing, DNA Repair

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